In a large skillet, cook sausage with onion and garlic until cooked through; drain. Add bell peppers, sundried tomatoes, and mushrooms. Cook for a few minutes or until peppers and mushrooms are tender. Add mozzarella and basil. Toss, put the lid on and let the cheese melt. Don't heat for too long or the cheese will get stringy. Sprinkle with parmesan cheese. Serve in tortillas with marinara sauce on the side for dipping.